This invention relates to a burn through and flame propagation resistant layer or covering for use in thermal and acoustical insulation systems, such as, but not limited to, those used in commercial aircraft. Preferably, for many applications such as commercial aircraft, the burn through and flame propagation resistant layer is also water vapor transmission resistant. The invention can be used as a layer or covering, e.g. interleaved between, laid over, or laid behind layers of thermal and acoustical insulation material or as a covering or bag for partially or totally encapsulating one or more layers of thermal and acoustical insulation material. While the burn through and flame propagation resistant layer or covering of the present invention is particularly well suited for aircraft applications, especially when the layer or covering is also water vapor transmission resistant, the burn through and flame propagation layer or covering may also be used for other applications where layers or coverings having these properties are needed or desirable.
The Notice of Proposed Rule-making expected to be issued by the Federal Aviation Administration (FAA) in the near future will require thermal and acoustical insulation blanket systems in commercial aircraft to provide improved burn through protection and flame propagation resistance. These systems typically include thermal and acoustical insulation blankets encapsulated within a film covering or bag. As the thermal and acoustical insulation systems are currently constructed, the burn through regulations primarily affect the contents of the insulation systems bags and the flame propagation resistance regulations primarily affect the film coverings used to fabricate the bags. Previous development work by a number of manufacturers has addressed the burn through resistance of the insulation within the bags or the flame propagation resistance of the film coverings used to fabricate the bags housing the insulation. However, no current system has solved both problems in the same product while providing the properties and low costs necessary for widespread commercial acceptance. Some of the systems currently being proposed are outlined in the following paragraphs.
With regard to burn through resistance one proposed system would utilize one or more layers of a nonwoven mat, made of fibers commercially available from The 3M Company of St. Paul, Minn. under the trade designation xe2x80x9cNEXTELxe2x80x9d as a fire barrier in the insulation blanket. The mat weighs 65 g/m2 and costs $15.00/m2 or more. Flame propagation issues still have to be addressed in connection with the film covering material.
With regard to flame propagation resistance, one proposed system would use a reinforced metallized polyvinylfluoride film covering manufactured by Facile Holdings, Inc. of Paterson, N.J., under the trade designations xe2x80x9cINSULFAB 330(copyright) or INSULFAB 331(copyright)xe2x80x9d. The reinforced metallized polyvinylfluoride film provides flame propagation resistance to the system but weighs 44 g/m2 and costs about $9.00/m2 compared to the reinforced polyester film covering currently used to fabricate the bag which weighs 25 g/m2 and costs about $2.70/m2.
Another proposal for flame propagation resistance is a system which would use reinforced polyimide film covering material manufactured by Orcon Corporation under the trade designation xe2x80x9cKN-80(copyright)xe2x80x9d. The reinforced polyimide film covering material provides flame propagation resistance to the system but weighs 50 g/m2 and costs about $13.00/m2 compared to the reinforced polyester film covering currently used to fabricate the bag which weighs 25 g/m2 and costs about $2.70/m2. Alone, this reinforced polyimide film covering does not provide significant burn through resistance.
The preferred burn through and flame propagation resistant layer or covering of the present invention, which is also water vapor transmission resistant, provides a solution, in a single light weight product, to both the burn through and the flame propagation requirements for light weight, thermal and acoustical insulation systems (such as those to be used in commercial aircraft) while also providing the water vapor transmission resistance required by such insulation systems. Furthermore, the burn through, flame propagation and water vapor transmission resistant layer or covering of the present invention can be easily incorporated into such insulation systems without the need to redesign the individual components of the system, e.g. by making the bag that contains or houses the insulation of the system from the covering of the present invention. Typically, the individual thermal and acoustical insulation components used to insulate aircraft fuselages are specifically designed at considerable cost to very close tolerances (e.g. length, width, thickness, and configuration) to precisely fit each specific portion of the fuselage. Thus, the ability to incorporate the burn through, flame propagation and, preferably, water vapor transmission resistant layer or covering of the present invention into such insulation systems without the need to redesign the individual components of the system is a valuable characteristic of the present invention.
One preferred embodiment of the burn through, flame propagation and water vapor transmission resistant system of the present invention includes a layer or covering which includes a sheet of burn through and flame propagation resistant paper made of aramid fibers, mica flakes, and aramid fibrid binder; and a sheet of water vapor transmission and flame propagation resistant polymeric film which has a major surface bonded to one major surface of the sheet of burn through and flame propagation resistant paper to form a laminated sheet. The laminated sheet may include a second sheet of polymeric film bonded to the other major surface of the burn through and flame propagation resistant paper.
The laminated sheet may also have a scrim layer incorporated into or bonded to the sheet or one of the sheets of the polymeric film and/or the sheet of burn through and flame propagation resistant paper to add strength to the laminated sheet, especially puncture and tear resistance. Furthermore, the sheet of polymeric film or, when two sheets of polymeric film are used, one of the sheets or both sheets of polymeric film in the laminated sheet may have a second major surface coated with a heat or ultrasonically sealable adhesive (hereinafter xe2x80x9ca heat sealable adhesivexe2x80x9d) for securing the laminated sheet: to itself or to another laminated sheet to form a covering, envelope, or bag for containing or encapsulating an insulation material; to an insulation layer; or to a structure, such as the skin, framework and/or the trim panels of an aircraft fuselage.
When the burn through and flame propagation resistant laminated sheet is also water vapor transmission resistant and the laminated sheet is formed into a covering, such as a bag or envelope, that partially or totally encloses or encapsulates one or more layers of thermal and acoustical insulation material, such as lightweight, flexible, glass fiber blankets or sheets of polyimide foam, the covering, envelope or bag formed from the laminated sheet serves to inhibit water vapor transmission during normal service and to inhibit both burn through and flame propagation in the event of fire. When the burn through and flame propagation resistant laminated sheet is also water vapor transmission resistant, the laminated sheet may also be used between layers or as a covering for one or more layers of lightweight, flexible, thermal and acoustical insulation material in an insulation system to inhibit water vapor transmission during normal service and to inhibit both burn through and flame propagation in the event of fire. For example, the laminated sheet may be used in a xe2x80x9cwallpaperxe2x80x9d application as a covering or layer that is located intermediate insulation material in fuselage wall cavities and the outer skin of an aircraft fuselage (as an outboard layer of an insulation system) or intermediate insulation material in fuselage wall cavities and the interior aircraft trim panels (as an inboard layer of an insulation system).
As an alternative to the laminated sheet described above, the burn through, flame propagation and, preferably, water vapor transmission resistant layer or covering of the present invention may be a sheet of burn through and flame propagation resistant paper made of aramid fibers, mica flakes, and aramid fibrid binder which is treated with a heat and/or ultrasonic sealable, moisture and flame propagation resistant polyvinylfluoride water based emulsion. As with the burn through, flame propagation and, preferably, water vapor transmission resistant laminated sheet described above, the treated sheet of burn through and flame propagation resistant paper can be used as a covering to contain thermal and acoustical insulation material (e.g. formed into a bag or envelope), can be used as a layer located intermediate layers of insulation material, or as a covering over one or more layers of such insulation material. The treated sheet of burn through and flame propagation resistant paper can have a scrim sheet or layer bonded to a major surface of the paper, preferably, by the heat sealable, moisture and flame propagation resistant polyvinylfluoride water based emulsion, to add strength, especially puncture and tear resistance.
The burn through, flame propagation and water vapor transmission resistant layer or covering of the present invention when used in a thermal and acoustic insulation blanket system for commercial aircraft passes the FAA medium scale burn through test; passes the flame propagation test; and preferably, has a water vapor permeability in perms of 4.0 or less and more preferably, of 2.5 or less. Preferably, the burn through, flame propagation and water vapor transmission resistant layer or covering of the present invention meets the material specifications of The Boeing Company of Seattle, Wash. for burst strength and puncture resistance having a minimum burst strength of 23 pounds per square inch (23 lb/in2) (Class 1 Film BMS 8-142) and has a minimum puncture resistance of 2 pounds. In simulated aircraft fuselage tests, aircraft thermal and acoustic insulation systems, using bags or envelopes for containing the insulation blankets made from the burn through, flame propagation and water vapor transmission resistant layers or coverings of the present invention, demonstrate heat and sound transmissions which are equivalent to current systems.
The burn through test referred to herein is the new Federal Aviation Administration (FAA) medium scale burn through test as presently defined (May 22, 2000) by the www.fire.tc.faa.gov web site (herein referred to as xe2x80x9cthe FAA medium scale burn through testxe2x80x9d). The FAA medium scale burn through test subjects the hot or outboard side major surface of a test sample to the flame of an oil burner that generates a temperature of approximately 1100xc2x0 C. The discharge end of the oil burner nozzle is positioned 10 centimeters (10 cm) from and directed toward the hot side major surface of the sample and generates a pulsating flame front. The FM medium scale burn through test measures the cold or inboard side heat flux at two specific locations on the cold side of the sample. To pass the FAA medium scale burn through test the sample must prevent both visible burn through and a cold side heat flux exceeding 2.0 Btu/ft2 for four minutes.
The flame propagation test referred to herein uses heat from a radiant panel and a pilot flame and is performed similarly to the current ASTM E 648 test procedures and performance criteria. Like the FM medium scale burn through test, the flame propagation test (hereinafter referred to as xe2x80x9cthe flame propagation testxe2x80x9d) is defined on the www.fire.tc.faa.gov web site. In the flame propagation test a pilot flame is applied at a zero point, for a period of fifteen seconds, to a horizontally oriented sample sheet. To pass the test, the flame must not propagate more than two inches beyond the point of contact (the zero point) between the pilot flame and the sample sheet and the sample sheet must not support continued combustion after the pilot flame is removed (there can be on evident flaming after the pilot flame is removed.